Drilling highly deviated and horizontal wells has been known for decades, and various methods and apparatus have been employed more or less successfully. Emphasis on horizontal drilling has been cyclical and dependent upon the price level of oil, gas and other natural resources which may be recovered via the use of such techniques.
Horizontal drilling apparatus, and particularly apparatus which can be precisely controlled as to depth and azimuth or direction are very useful in recovering natural resources from subterranean formations which are of nominal thickness, as conventional vertical drilling techniques can only intersect such formations for a short interval (i.e., the formation thickness) so that the total surface area of the wellbore exposed to the formation and from which the natural resources may be recovered is extremely limited. On the other hand, a horizontal drilling apparatus, and particularly a steerable apparatus, can not only intersect the target formation but follow its path under the earth for hundreds or even thousands of feet, exposing the wellbore to a formation surface area many orders of magnitude greater than that achievable by conventional vertical drilling techniques. The falling and stabilization of oil prices in recent years at levels less than half of those encountered in the early 1980's has generated renewed interest in horizontal drilling as a means to maximize production from each well drilled, and therefore the operator's profit margin.
In addition to natural resource recovery applications of horizontal drilling, enactment of environmental legislation during the past two decades and enhanced monitoring and enforcement activities by federal and state governments has opened vast new fields of opportunity for a compact, easily transportable, economical horizontal drilling method and apparatus which can be employed to drill monitoring, injection, recovery and barrier wells in the vicinity of land fills, industrial sites, toxic waste repositories and other locations in which the natural environment has or may become contaminated through man's intentional actions or neglect. Subsurface monitoring and remediation techniques for contaminated sites are in their infancy, but in most instances require the ability to not only surround but also to reach under the suspected or confirmed contaminated plume or volume of earth from a remote position outside of the zone of contamination. Moreover, the vast size of many sites requires the drilling and completion of hundreds if not thousand of wells at a single location.
Existing methods and apparatus for horizontal drilling have been developed for oil recovery, mineral recovery and for the installation of cables and pipes under rivers, swamps, highways, building and other natural and man-made obstacles. While potentially applicable to environmental remediation activities, they are generally expensive to build and to use, and in many instances lack the ability to follow a relatively precise path. This latter point is extremely important when drilling at very shallow depths, as inadvertently drilling from below into a plume of contaminated earth may result in catastrophic groundwater contamination where none previously existed. Drilling systems which can complete a well as it is being drilled are extremely desirable, from a rig time cost saving standpoint and, more important, because subsurface formations at shallow depths are generally unconsolidated and therefore lack inherent physical strength against collapse of the wellbore once the drill string is withdrawn. Such collapse requires redrilling of the well and also may enhance flow of contaminants from a contaminated but previously isolated zone above the wellbore, thus aggravating the existing problem.
In short, there has been a long felt and ever increasing need for a compact, economical, easily transportable horizontal drilling system which can be effectively used at environmental monitoring and remediation sites.